Virtualization allows, among other things, many computer environments, such as general desktop environments, database servers, web development platforms, etc., to be implemented through software and/or hardware as virtual machines within host computing devices. A virtual machine may comprise its own file structure, virtual hard disks, partitions, operating system (e.g., a guest operating system), applications, data files, and/or configuration, for example. As such, the virtual machine may function as a self-contained computing environment even though it may be an abstraction of underlying software and/or hardware resources (e.g., a virtual machine may be stored as one or more virtual structures, such as a virtual machine disk, within physical storage). That is, the virtual machine may be a software implementation of a physical computing machine that has normal operational functionality of the physical computing machine. For example, a host computing device may comprise virtual machine host software (e.g., a hypervisor) configured to host and manage virtual machines. The virtual machine host software may allow a user to interface and interact with a hosted virtual machine. For example, the user may interact with a guest operating system and/or applications of the hosted virtual machine through the virtual machine host software.
A virtual machine, or one or more portions thereof, may be stored as one or more virtual structures that may be stored within underlying physical storage of one or more storage devices. A virtual structure may comprise virtual storage, such as a virtual hard disk (e.g., a virtual machine disk (.vmdk) format, a virtual hard disk (.vdh) format, etc.). The virtual storage may be a level of abstraction from the storage device (e.g., underlying physical storage) because the virtual storage may store the virtual machine data according to a virtual data format that may not be dependent upon a storage data format specifying how data, such as the virtual structure, is stored within the storage device. For example, a guest operating system of a virtual machine may store a user created text document according to a virtual data format within a virtual hard disk of a virtual structure (e.g., the user created text document may be stored within virtual data blocks of 512 bytes). The virtual data format may be independent of a storage data format used by a storage device to store the virtual structure (e.g., the virtual structure may be stored within physical data blocks of 4096 bytes). That is, the virtual data format (e.g., how virtual machine data is stored within a virtual structure) may be a level of abstraction from the storage data format (e.g., how the data, such as the virtual structure, is stored within underlying physical storage).
Unfortunately, storing virtualized data (e.g., virtual machine data within a virtual structure) within underlying physical storage may result in misalignment. For example, a guest operating system of a virtual machine may store virtual machine data according to a virtual data format within the virtual structure (e.g., the virtual data format may specify that a virtual file system of the virtual machine stores data within 512 byte blocks starting at an offset of 63 blocks within the virtual structure). However, the virtual structure may be stored within a storage device (e.g., underlying physical storage) according to a storage data format (e.g., the virtual structure may be stored within physical data blocks of 4096 bytes). If the virtual data format and the storage data format align, then virtual data blocks may be stored within corresponding underlying physical data blocks without overlapping into additional underlying physical data blocks (e.g., virtual data blocks may span no more than one underlying physical data block).
If the virtual data format and the storage data format do not align, however, then virtual data blocks may end up being stored across one or more additional underlying physical data blocks (e.g., a virtual data block may span more than one underlying physical data block). Thus, if a virtual data block is misaligned, then an I/O operation for the virtual data block may entail accessing more than one underlying physical data block (e.g., a first portion of the virtual data block may be read from a first underlying physical data block and a second portion of the virtual data block may be read from a second underlying physical data block). Such additional I/O operations may result in performance degradation. For example, access to a guest operating system and/or user data of a virtual machine may take twice as long because more than one I/O operation to underlying data storage may need to be performed to access a single virtual data block due to the misalignment.